It is well known that moisture has adverse effects on the properties of optical components. The split ratio of optical splitters, for example, may be influenced by the presence of moisture, and in optical connectors moisture may lead to increased losses. The sealing of optical components against moisture and other environmental influences, in other words environmental sealing, is therefore highly desirable.
It has been proposed to environmentally seal individual optical components. This is, however, expensive and not always effective.
In the case of electrical components it is known to seal an entire circuit by enclosing it in a flexible, moisture-resistant bag. WO 94/18815 (Ericsson), for example, discloses a casing for flexibly enclosing electronic circuitry. The casing comprises a laminate consisting of metal and plastic sheets. Two sheets of laminate are joined to form an envelope in which electronic circuitry may be accommodated. Electrical conductors pass through the joint region of the laminate.
Although such an arrangement may be effective for sealing electronic circuits, it is less suitable for optical components or circuits. The applicant has found that optical fibres, unlike electrical conductors such as copper wires, should not be passed through the joint region of the laminate without additional measures. Copper wires (or other electrical conductors) may be bent under almost any angle without affecting their conductive properties. Optical fibres however, while being more flexible than copper wires, should not be bent under the minimum bending radius at which light losses occur (usually approximately 3 cm), and certainly not under the minimum bending radius at which they suffer permanent damage. In addition, optical fibres are made of glass which has different sealing properties to metal.
The applicant's earlier GB patent application No. 0110366.2 discloses a method of sealingly enclosing a space into which optical fibres are fed by a accommodating a portion of at least one optical fibre between two sealing strips and applying pressure or heat to the strips to sealingly enclose the fibre, followed by the step of placing the seal formed by the sealing strips in the opening of a container and applying heat and/or pressure to the container to seal the opening onto the strips. This method is particularly suitable for providing a moisture resistant container enclosing at least one optical component with fibres fed through the seal for optically connecting the enclosed component with other components on the exterior of the enclosure.
One disadvantage associated with this method of sealing is that the fibre or fibres are fed into the enclosed space along an edge of the container. The fibre or fibres extend substantially perpendicular with respect to the longitudinal direction of the sealed edge such that he fibres extend perpendicularly from and with respect to the sealed edge of the enclosure: This can be particularly disadvantageous in applications where there is a requirement to route the fibre back over the surface of the enclosure, for example when storing the enclosure and fibre ends in a fibre optic organiser tray or in a tray type container closed by a closure member in the form of an organiser tray, since the fibre must have a minimum bend radius which results in the fibre extending beyond the edges of the enclosure.
There is a requirement therefore for a method of sealingly enclosing a space into which at least one optical fibre is fed which avoids the problem of the fibre exiting a sealed edge of a sealed enclosure, and a further requirement for a more compact enclosure where the fibre ends can be stored on the surface of the enclosure without extending beyond the edges thereof.